1. Field of the Invention
The present invention is directed generally to an apparatus for conveying finely powdered toner material from a reservoir and, in particular, to an apparatus for conveying toner in a printer or copier.
2. Description of the Related Art
In printers or copiers that electrophotographically apply toner to a carrier material, the toner is stored in a reservoir and is supplied to a developer station of the printer or copier by a conveyor apparatus. For example, an underpressure or suction is generated, which is used to suction the toner from the reservoir and move it to the developer station. A toner/air mixer is generated which is conveyed through channels, tubes, and hoses by the underpressure to a separator in which the air is separated from the toner/air mixture to supply the toner to the developer station. Blockages in the channels, tubes and hoses often occur in such underpressure systems. Although the probability of a blockage is reduced by increasing the velocity of the toner/air mixture through the channels, tubes and hoses, this causes mechanical and electrostatic changes to occur in the toner, which much be accepted as a tradeoff.
Mechanical conveyor systems are also known in which a conveyor worm screw or paddles are used to move the toner. Such mechanical systems are effective for conveying the toner only over short conveying distances and with limited dependability. Moreover, the toner is damaged by the friction and compression imposed on the toner of such mechanical conveyors. To empty the reservoir as completely as possible without leaving toner residue behind, mechanical shakers or beaters are utilized; however, these compress the toner and make it more difficult to convey the toner by underpressure, for example. The shaking and beating of the toner container also causes physical changes or damage to the toner.
In Japanese Patent Document JP 61-151675 A and the corresponding English abstract in Patent Abstracts of Japan, P-521, 1986, Vol. 10, No. 354, is disclosed a means for conveying toner in which gas flows under pressure along a conduit. A suction channel that projects into the reservoir for the toner branches off from the conduit. Toner material mixed with the gas is extracted through the suction channel.
In the publication patent abstracts of Japan P 483, 1986, Vol. 10, No. 223, which is the abstract of Japanese Patent Document JP 61-59 464 A, is disclosed a toner delivery means wherein a part of the conveyed toner/gas mixture is branched off and then returned into the toner reservoir. The branching of the toner/gas mixture is intended to promote suction efficiency. Nothing in this document teaches to provide a fluidizing unit which fluidizes the toner in the immediate proximity of the end of the suction pipe.
German Patent Document DE 36 33 599 A1 discloses a means for filling toner from a transport container into a toner reservoir. The air flows around the end of an ascending pipe as disclosed in an exemplary embodiment shown in FIG. 3 of the reference. To keep the toner in an easily conveyed condition, a shaker is provided in the proximity of the end of the ascending pipe, the shaker shakes the toner so that it is conveyed through a toner sieve through intake openings and then proceeds into the ascending pipe through openings in the pipe. Nowhere is it shown in this reference that a fluidizing unit is provided which places the toner in a fluid-like condition.
German Patent Document DE 35 46 231 A1 discloses a powder spray gun for an electrostatic powder coating. The spray gun works according to the Venturi effect, where a gas stream in a suction channel generates an underpressure, or suction, that conveys the powder into the main gas stream, where it is mixed with the gas.